In fixed-bed hydroprocessing reactors, gas and liquid reactants (e.g. hydrogen and a hydrocarbonaceous feedstock) flow downward through one or more beds of solid catalyst extrudates. As the reactants flow downward through the catalyst beds, the reactants react to produce the desired products. Gas phase reactants such as hydrogen are consumed, and heat is generated by the catalytic reactions.
FIG. 1 is a cross-sectional schematic diagram of a conventional vertical, down-flow reactor such as the one disclosed in U.S. Pat. No. 3,824,080 to Smith et al., issued Jul. 16, 1974. The reactor 1 includes a reactor vessel 2 having upper and lower catalyst zones 3 and 4, respectively, and a quench zone 5 there between.
A liquid hydrocarbonaceous feedstock is introduced into the vessel 2 via line 6 through inlet nozzle 7. The feedstock strikes a splash plate 8 distributing the feedstock across a nozzle distribution assembly 9 adapted to uniformly spray the feedstock across the top of the upper catalyst zone 3.
The effluent from the upper catalyst zone 3 passes to the quench zone 5. As feedstock flows downward through the catalyst zones 3,4, the feedstock contacts catalyst extrudates and reacts to produce the desired products. Gas phase reactants such as hydrogen are consumed, and heat is generated by the catalytic reactions.
Controlling the temperature of the feedstock as it travels downward through the vessel 2 is important to ensure the quality and quantity of product yield is maximized toward the target product(s). These features are accomplished in the quench zone 5 wherein: (1) hydrogen quench gas is injected into the vessel 2 via line 10, (2) quench hydrogen gas is mixed with the liquid effluent flowing down from the upper catalyst zone 3 using a mixing device 11, and (3) a quench zone nozzle distribution assembly 12 uniformly sprays the quenched feedstock across the top of the lower catalyst zone 4.
The quenched feedstock flows downward through second catalyst zone 4 wherein reactants undergo additional catalytic reactions. Effluent from the second reaction zone 4 enters a conventional outlet cap 13, and the reaction effluent exits the reactor vessel 2 via line 14.
In a conventional reactor, such as the reactor illustrated in FIG. 1, the lowermost or bottom catalyst bed can be supported above the outlet using a horizontal catalyst tray (illustrated as element 15 in FIG. 1). However, such designs produce empty or dead spaces at the bottom of the reactor. In addition, the amount of active catalyst that can be loaded into the lower catalyst bed is limited by the static load limits of the horizontal tray. This limitation is significant because available feedstocks are become increasingly disadvantaged, requiring more hydroprocessing which, in turn, necessitates loading more catalyst material into existing reactors.
Other conventional reactors substitute a bed of inert material, such as inert ceramic spheres, for the lower bed horizontal catalyst tray. (See, drawing element 13 of FIG. 1, US 2006/0163758 to Muller, published Jul. 27, 2006). While use of inert materials as the lower catalyst bed support allows for the loading of more active catalyst into the lower bed as compared to a conventional horizontal tray, such inert bed supports add substantial additional costs. In addition, over time the inert materials breakdown, producing fines that must be collected and removed downstream from the reactor, and requires periodic replacement of the inert material.
Accordingly, there is a continued need for lower catalyst bed support systems that reduce or eliminate empty or dead spaces at the bottom of conventional hydroprocessing reactors. In addition, there continues to be a need for catalyst bed support systems that allow refiners to load increasing amounts of catalyst materials into a reactor, without resorting to use of inert catalyst support particle beds, which degrade over time and add significant operating costs to the refinery.